1. Field of the Invention
The present disclosure generally relates to a frequency-to-voltage converter and, more particularly, to a frequency-to-voltage converter without a low pass filter circuit.
2. Description of the Related Art
A frequency-to-voltage converter can receive and convert a pulse-type of frequency signal into a voltage signal in positive correlation. The frequency-to-voltage converter can be widely used in some fields such as rotational speed measurement and mechanical control. For example, when the frequency-to-voltage converter receives a frequency signal of a rotating electric motor, the generated voltage signal can be used not only to represent the rotational speed of the electric motor, but also to serve as a control signal of the electric motor.
A conventional frequency-to-voltage converter generally includes a comparator circuit, an intergrator circuit and a low pass filter circuit. When the comparator circuit receives the frequency signal, the comparator circuit can be triggered by the pulses of the frequency signal to continuously generate a triggering signal. The intergrator circuit can be triggered by the triggering signal to generate the voltage signal. Since the voltage signal of the intergrator circuit is analogous, the voltage signal should be filtered by the low pass filter circuit to reduce the ripple of the voltage signal, so as to increase the accuracy in retrieving the voltage signal.
Generally, the low pass filter circuit is formed by resistors and capacitors for performing the filtering function. The resistors and capacitors have a time constant. If the time constant is large, the low pass filter circuit will have a better performance. However, the overall transition time will be adversely longer. As a result, the voltage signal will not be able to instantly reflect the change of the rotational speed of the electric motor. To the contrary, if the time constant is small, the transition time will be shorter but the ripple will be larger. This causes an inaccurate voltage value of the voltage signal.
In light of the disadvantage of the conventional frequency-to-voltage converter where it is difficult to ensure proper transition time and ripple magnitude at the same time, it is necessary to provide a novel frequency-to-voltage converter which is able to do so.